Characterization of splash droplets from different surfaces with a phase doppler particle analyzer

A phase doppler particle analyzer (PDPA) was used to obtain information nee ded to characterize water splashed from various surfaces with the aim of ex panding our knowledge of the spore dispersal process. Simulated rain was ge nerated with flat-fan nozzle which produced a cumulative volume distributio n similar to that of natural rains with 45 mm/h intensity. Thirteen differe nt surfaces exhibited large differences in size distribution and total mass of splashed droplets produced. Surfaces were: bare soil, straw, plastic, s and, deep water, loosely stacked strawberry leaflets, leaflets placed horiz ontal on soil, healthy and rotten (diseased) strawberry fruits, and four co mbinations of height and planting density of a sudangrass cover crop. In ge neral, sand, straw, leaflet, and fruit surfaces had low splash responses, w hile the water surface and the plastic cover had the highest responses. Fro m 0.8% (sand) to 41.5% (plastic) of the incident rain mass was splashed >1 cm above the surfaces. For all surface treatments, droplet size distributio n was positively skewed, with many more small droplets (<1 mm diameter) tha n large ones; however, larger droplets provided a greater contribution to t he total mass than the smaller ones, resulting in bimodal volume distributi on. Differences among treatments were observed for some percentiles of the cumulative volume distribution of droplets, even when the shapes of the cur ves were similar. The water treatment and the tall sudangrass at high plant ing density had the largest mean D-50 values (volume median diameter). The straw, leaflet, sand, and fruit surfaces had the smallest D-50 values. Perc entiles of the mass distribution reflected differences in the movement of s pores across different surfaces, even when the mass of water splashed was f ixed. Mean number Aux density (N-D) and mean mass flux density (R) varied c onsiderably among the surface treatments, with the plastic cover having sig nificantly higher N-D and R values than those for the other treatments. Res ults validated previous findings regarding the splash from selected surface s, showed that a cover crop affected splash, indicated that plant parts dif fered in the properties of produced splash droplets, and showed how splash dispersal of plant pathogenic fungi could be affected by a wide range of su rface conditions. (C)0 1999 Elsevier Science B.V. All rights reserved.